Do plastic screens prevent the spread of COVID-19?

Nestled between restaurant diners, placed in front of supermarket cashiers, inserted between office desks and even installed at the Houses of Parliament – since the outbreak of the pandemic, there are few areas of life that remain unsegregated by a transparent screen.

But how effective are plastic barriers in preventing the transmission of COVID-19?

A Whitehall document seen by Politico London Playbook in June advised ministers against the use of barriers, arguing that the partitions could in fact exacerbate transmission by blocking airflow that helps to disperse aerosols.

Speaking with OT in April, AOP clinical director, Dr Peter Hampson, highlighted debate around the benefits of using barriers to stop viral spread. 

“While the screens help when dealing with two metre droplets, they aren’t necessarily great if particles are floating in the air. This is where ventilation becomes key as good air flow can dilute the virus,” he explained.

Current NHS England guidance for close contact services includes barriers in the use of additional infection control measures that can be used when two metre social distancing is not possible.

Guidance for workers in retail environments exempts staff from wearing a face mask if a physical barrier between members of the public and employees is in place.

OT spoke with Howard Stone, a professor of mechanical and aerospace engineering at Princeton University, for his thoughts on whether evidence on the effectiveness of physical barriers in preventing the transmission of COVID-19 backs up their ubiquity.

Stone has contributed to research exploring how flows created during breathing and speaking could contribute to the spread of COVID-19 by asymptomatic individuals.

How understanding of COVID-19 transmission evolved

Stone shared that plastic barriers became common due to emphasis at the beginning of the pandemic around the role of bigger droplets in spreading COVID-19.

Because of this focus, people were encouraged to regularly clean surfaces, maintain social distance and put in place measures like barriers when social distancing was not possible.

However, current evidence suggests smaller droplets – called aerosols – which linger in the air have a significant role to play in the transmission of the virus.

“When you exhale – whether that is breathing, speaking, singing, laughing – you produce droplets. The normal view of the bigger droplets is that they fall due to gravity, like when you drop an orange. A barrier would stop them. The smaller droplets stay in the air. They just follow where the air goes,” Stone said.

“We know this because we smell perfume and we see smoke – that can easily pass around barriers. Whether or not that happens, and how long it takes, depends on the overall air flow in the room which is dictated in a significant part by the ventilation in the room,” he added.

The normal view of the bigger droplets is that they fall due to gravity, like when you drop an orange. A barrier would stop them. The smaller droplets stay in the air

 

Stone added that while physical barriers provide a degree of protection, the focus should be on wearing masks, increasing ventilation, ensuring air flow and socialising outdoors if possible.

“The picture now is that everything you can do to increase ventilation with fresh air to effectively dilute the virus so that you breathe in less contaminated air is the best strategy,” he said.

“Where possible, if you are not wearing a mask and not vaccinated, don’t share air with people,” Stone added.

Plastic: not-so fantastic

The increasing use of plastic barriers also has environmental implications.

Research published in the Journal of the Royal Society of Medicine in March highlighted that the daily carbon footprint of personal protective equipment (PPE) distributed by NHS England during the first six months of the pandemic was equivalent to 244 return flights from London to New York.

Writing in the British Medical Journal in the same month, trainee anaesthetists and sustainability fellows, Li Fang and Annie Pinder, argued alongside colleagues against ‘hygiene theatre’ – the conspicuous use of PPE in low-risk settings.

“With pandemics anticipated to occur more frequently in the future, research must focus on reducing the environmental impact of PPE,” they shared.

“The scientific basis for PPE use must be regularly re-examined. Notably, ‘contact precautions’ have featured in PPE policies since the pandemic began, but prevailing evidence indicates that surface transmission of SARS-CoV-2 is low with effective handwashing,” the authors highlighted.